ESBD analysis - Applying the study of deformation and recrystallization of metallic materials

The term "microstructure" covers both morphological texture, i.e. grain size and shape, and crystallographic texture (distribution of crystallographic orientations). Controlling these two parameters is crucial to optimizing the mechanical, magnetic and electrical properties of metallic materials.

X-ray or neutron diffraction provides a global measure of the orientation distribution in the polycrystal. But this crystallographic texture cannot be correlated with the microstructure. This highlights the need for experimental techniques capable of characterizing these different parameters locally and simultaneously.

Several methods can be used to measure local orientations within a microstructure. But one of them has become a widespread tool in both academic and industrial laboratories: Electron BackScattered Diffraction (EBSD) in a scanning electron microscope (SEM).

Since the 1990s, with a fully computerized version, it has been possible to measure orientation maps (reconstruction of the microstructure from crystallographic orientation measurements) and phases.

In addition to the crystallographic texture itself, these mappings provide a wealth of other data, such as the distribution of grain boundaries, intragranular orientation gradients, etc. As a result, the analysis of deformation structures, recrystallization, phase transformation and grain growth is greatly facilitated.

Texture analysis can be local, but also global, i.e. comparable to that estimated by X-ray or neutron diffraction, provided a sufficient number of grains are considered.

The quality of diffraction patterns is important, as they can be an indicator of the material's work hardening and a means of estimating the fraction of dislocation-free grains in a partially recrystallized material. A detailed analysis of these patterns provides access to the measurement of elastic and plastic deformations.

This experimental technique has also become an indispensable tool for microstructure simulation. It provides input data for simulation (microstructure, texture, energy stored during deformation, etc.) and validates simulated results in terms of deformation, recrystallization, grain growth, etc.

EBSD, its possibilities and examples of results obtained on metallic materials are presented in two articles:

• [M 4 138] . It describes the principle of EBSD and the...